Other Minds

If we can make contact with cephalopods as sentient beings, it is not because of a shared history, not because of kinship, but because evolution built minds twice over. This is probably the closest we will come to meeting an intelligent alien.

In an animal like us, a large proportion of the energy taken in as food, nearly a quarter in our case, is spent just keeping the brain running.

The “Cambrian explosion” began around 542 million years ago. In a relatively sudden series of events, most of the basic animal forms seen today arose. These “basic animal forms” did not include mammals, but did include vertebrates, in the form of fish. They also included arthropods – animals with an external skeleton and limbs with joints, such as trilobites – along with worms, and various others.

This interaction between perception and action is also seen in what psychologists call perceptual constancies. For us, an object can remain recognizable as the same object while our viewpoint on it changes. As you move closer to or further from a chair, it does not usually seem to grow, shrink, or move, because you tacitly compensate for the changes in appearance that are due to your actions, along with some changes that are not due to you, such as shifts in lighting conditions, and so on.

The senses can do their basic work, and actions can be produced, with all this happening “in silence” as far as the organism’s experience is concerned. Then, at some stage in evolution, extra capacities appear that do give rise to subjective experience: the sensory streams are brought together, an “internal model” of the world arises, and there’s a recognition of time and self.

simple example is writing something down, a note to yourself, which you will read later. You act now, changing the environment, and later you will perceive the results of your act. This will enable you to do something, at that later time, that makes sense given what you know now.

A tree grows by the multiplication of small units – branching stems – that can each reproduce on their own and, if cut and transplanted, can give rise to another tree.

Memory in animals has several varieties. An important kind of memory in human experience is episodic memory – memory of particular events, as opposed to memory of facts or skills. (Your memory of your last birthday is an episodic memory; your memory of how to swim is a procedural memory, and your memory of the location of France is a semantic memory.)